Unfortunately yep you really need a new build to go higher floor. The reason you are struggling with mythic enemy is because crushing blow chance decreases as the rarity of the enemy increases here is the article : Crushing Blow - #5 by SteigerBox
If you dont mind take a look at my farm build
It can delete mobs and even mythic enemy if you can group them which you need to target for pack size map
If you want to keep crushing flames then you can change the frozen set and do some tweaking because many of the procs are warrior skills.Explore some stuff and do experiments on your own cause that what gives DQ joy to play 
You can keep your old build tho or take some inspirations on this build also you can search many other tips on the forum